The need to provide photographic film and paper with antistatic protection is well recognized in the photographic industry. Such protection is important since the accumulation of static charges as a result of various factors in the manufacture, finishing, and use of photographic elements is a serious problem. Accumulation of static charges can result in fog patterns in photographic emulsions, various coating imperfections such as mottle patterns and repellency spots, dirt and dust attraction which may result in the formation of "pinholes" in processed films, and a variety of handling and conveyance problems.
To overcome the problem of accumulation of static charges, it is conventional practice to provide an antistatic layer (i.e., a conductive layer) in photographic elements. A very wide variety of antistatic layers are known for use in photographic elements. For example, an antistatic layer comprising an alkali metal salt of a copolymer of styrene and styrylundecanoic acid is disclosed in U.S. Pat. No. 3,033,679. Photographic films having a metal halide, such as sodium chloride or potassium chloride, as the conducting material, in a hardened polyvinyl alcohol binder are described in U.S. Pat. No. 3,437,484. In U.S. Pat. No. 3,525,621, the antistatic layer is comprised of colloidal silica and an organic antistatic agent, such as an alkali metal salt of an alkylaryl polyether sulfonate, an alkali metal salt of an arylsulfonic acid, or an alkali metal salt of a polymeric carboxylic acid. An antistatic layer comprised of an anionic film forming polyelectrolyte, colloidal silica and a polyalkylene oxide is disclosed in U.S. Pat. No. 3,630,740. In U.S. Pat. No. 3,681,070, an antistatic layer is described in which the antistatic agent is a copolymer of styrene and styrene sulfonic acid. U.S. Pat. No. 4,542,095 describes antistatic compositions comprising a binder, a nonionic surface-active polymer having polymerized alkylene oxide monomers and an alkali metal salt. In U.S. Pat. No. 4,916,011, an antistatic layer comprising a styrene sulfonate-maleic acid copolymer, a latex binder, and an alkyl-substituted trifunctional aziridine crosslinking agent are disclosed. An antistatic layer comprising a vanadium pentoxide colloidal gel is described in U.S. Pat. No. 4,203,769. U.S. Pat. Nos. 4,237,194; 4,308,332; and 4,526,706 described antistats based on polyaniline salt-containing layers. Crosslinked vinylbenzyl quaternary ammonium polymer antistatic layers are described in U.S. Pat. No. 4,070,189.
Frequently, the chemicals in a photographic processing solution are capable of reacting with or solubilizing the conductive compounds in an antistatic layer, thus deleteriously affecting, by causing a diminution or complete loss of the desired antistatic properties. To overcome this problem, antistatic layers are often overcoated with a protective layer to chemically isolate the antistatic layer. In the case of backside (that is, the side opposite to the photographic emulsion layer), the protective layer for the antistatic layer may also serve to provide scratch and abrasion resistance. Typically, this protective layer is a glassy polymer with a glass transition temperature (Tg) of 70.degree. C. or higher that is applied from organic solvent-based coating solutions. For example, in the aforementioned U.S. Pat. No. 4,203,769 the vanadium pentoxide antistatic layer may be overcoated with a cellulosic protective layer applied from an organic solvent. U.S. Pat. Nos. 4,612,279 and 4,735,976 described organic solvent-applied protective overcoats for antistatic layers comprising a blend of cellulosic nitrate and a copolymer containing acrylic acid or methacrylic acid.
Due to environmental considerations, it is desirable to replace organic solvent-based coating formulations with water-based coatings that provide comparable physical and chemical properties in the dried film that can be obtained with organic solvent-based coatings. Aqueous-based backing layers and barrier layers for antistatic coatings have been described. For example, in Anderson, et al., U.S. Pat. No. 5,006,451, issued Apr. 9, 1991, it is disclosed that the use of a latex polymer barrier layer applied over a vanadium pentoxide antistatic subbing layer prevents the loss of antistatic properties after film processing. However, to adequately coalesce the latex (so as to provide an effective barrier layer) during the extremely short drying times typical of high speed film support manufacturing may require the use of significant concentrations of high boiling point organic solvents, "coalescing aids", in the coating formulation. Such coalescing aids may be partially volatilized when the barrier coating is dried and may subsequently recondense in cooler areas of the coating machine. This condensation of high boiling organic compounds can result in a variety of problems such as conveyance problems and various coating imperfections. Coalescing aids that remain permanently in a dried film may have an adverse effect on the physical properties of the layer.
Coatings for photographic applications must also provide required physical and chemical properties such as abrasion resistance and impermeability to aqueous film processing solutions using extremely thin layers. Typically these layers are less than 1 micron thick. Thus, film formation and film quality are especially critical. In addition, coating compositions for photographic film applications must not adversely affect any sensitometric responses (such as cause fogging of the photographic emulsion) or reduce the transparency of the processed film.